This relates to transmission protocols and more particularly, to a protocol for transmitting messages in a network that employs a collision-based protocol. The network may be an ad hoc network.
For various reasons, mobile ad-hoc networks are best served by a collision-based architecture, and at least in some applications it is desirable to employ a protocol with a two-level QoS scheme. In at least one form of collision-based networks, a unit that wishes to transmit listens to the common channel over which other units might be transmitting and when it has a message (e.g., a packet) to transmit and it determines that the channel is available, it proceeds to transmit the message. When the unit determines that the channel is unavailable, it obtains a delay measure (back-off interval), which typically is a random value within a predetermined range, waits for a time corresponding to the obtained back-off interval, and then again determines whether the channel is available. If so, the unit transmits the message. Otherwise, the unit again waits the same (or different) back-off interval and tries again.
One well known collision-based approach employs the 802.11 protocol. While the 802.11 protocol provides a QoS facility, the ability to have different QoS levels needs base stations to administer the protocol, but use of base stations is generally disfavored in mobile ad hoc networks because it is desirable to confer on these networks a highly alterable constitution. The desirable approach, therefore, is one that does not require the use of base stations.